Rail car ride quality program
An intense car body vibration, known as body wobble, had been reported in a passenger railcar operating over known track locations in country commuter routes. Sinclair Knight Merz was engaged to conduct a detailed on-track test program on a railcar to determine the nature and cause of the body wobble phenomenon.
Multi-channel data recording and computer animation enhance problem understanding
On-track testing was undertaken, involving the simultaneous recording of 24 channels of vibration signals from measurement locations on the car body, bogies and axle boxes. Post processing of the vibration data involved an innovative technique involving computer animation of the transient time history vibration responses obtained during body wobble events, giving a clear picture of the car and bogie dynamic deformations and interaction.
Load indicator measurements were also recorded to determine dominant transfer paths of dynamic loads from the bogies to the car body.
Body wobble mechanism clearly identified
The testing identified:
- A resonant torsional response of the car body at 8 Hz.
- The car body response being exited by a lateral bogie dynamic instability.
- A load transfer mechanism from the vibrating bogie, through the lateral damper to the traction centre, creating a moment to excite the resonant car body torsional response.
The test and evaluation program resulted in a detailed understanding of the body wobble vibration so that solution alternatives could be targeted.